day(08): add initial solution

Signed-off-by: Matej Focko <mfocko@redhat.com>

samples/day08.txt

@@ -0,0 +1,5 @@
+30373
+25512
+65332
+33549
+35390

src/bin/day08.rs

@@ -0,0 +1,144 @@
+use std::{cmp::max, collections::BTreeSet};
+
+use aoc_2022::*;
+
+use color_eyre::eyre::Result;
+use itertools::Itertools;
+use tracing::*;
+use tracing_subscriber::EnvFilter;
+
+type Input = Vec<Vec<i8>>;
+type Output = usize;
+
+fn count_in_rows(trees: &Input, counted: &mut BTreeSet<(usize, usize)>) {
+    trees.iter().enumerate().for_each(|(y, row)| {
+        row.iter().enumerate().fold(-1, |tallest, (x, tree)| {
+            if *tree > tallest {
+                counted.insert((x, y));
+            }
+
+            max(*tree, tallest)
+        });
+
+        row.iter().enumerate().rfold(-1, |tallest, (x, tree)| {
+            if *tree > tallest {
+                counted.insert((x, y));
+            }
+
+            max(*tree, tallest)
+        });
+    });
+}
+
+fn count_in_columns(trees: &Input, counted: &mut BTreeSet<(usize, usize)>) {
+    (0..trees[0].len()).for_each(|x| {
+        (0..trees.len()).fold(-1, |tallest, y| {
+            if trees[y][x] > tallest {
+                counted.insert((x, y));
+            }
+
+            max(tallest, trees[y][x])
+        });
+
+        (0..trees.len()).rev().fold(-1, |tallest, y| {
+            if trees[y][x] > tallest {
+                counted.insert((x, y));
+            }
+
+            max(tallest, trees[y][x])
+        });
+    });
+}
+
+fn part_1(input: &Input) -> Output {
+    let mut counted: BTreeSet<(usize, usize)> = BTreeSet::new();
+
+    count_in_rows(input, &mut counted);
+    count_in_columns(input, &mut counted);
+
+    counted.len()
+}
+
+fn in_range(trees: &Input, x: i32, y: i32) -> bool {
+    y >= 0 && y < trees.len() as i32 && x >= 0 && x < trees[y as usize].len() as i32
+}
+
+fn compute_scenic_score(trees: &Input, x: i32, y: i32) -> usize {
+    vec![(0, 1), (1, 0), (0, -1), (-1, 0)]
+        .iter()
+        .map(|&(dx, dy)| {
+            let max_height = trees[y as usize][x as usize];
+            let mut d = 1;
+
+            let mut visible = 0;
+
+            while in_range(trees, x + d * dx, y + d * dy) {
+                visible += 1;
+
+                if trees[(y + d * dy) as usize][(x + d * dx) as usize] >= max_height {
+                    break;
+                }
+
+                d += 1;
+            }
+
+            visible as usize
+        })
+        .product()
+}
+
+fn part_2(input: &Input) -> Output {
+    (0..input.len())
+        .flat_map(|y| {
+            (0..input[y].len()).map(move |x| compute_scenic_score(input, x as i32, y as i32))
+        })
+        .max()
+        .unwrap()
+}
+
+fn parse_input(pathname: &str) -> Input {
+    file_to_string(pathname)
+        .lines()
+        .map(|line| {
+            line.chars()
+                .map(|c| c.to_digit(10).unwrap() as i8)
+                .collect_vec()
+        })
+        .collect_vec()
+}
+
+fn main() -> Result<()> {
+    tracing_subscriber::fmt()
+        .with_env_filter(EnvFilter::from_default_env())
+        .with_target(false)
+        .with_file(true)
+        .with_line_number(true)
+        .without_time()
+        .compact()
+        .init();
+    color_eyre::install()?;
+
+    let input = parse_input("inputs/day08.txt");
+
+    info!("Part 1: {}", part_1(&input));
+    info!("Part 2: {}", part_2(&input));
+
+    Ok(())
+}
+
+#[cfg(test)]
+mod day_08 {
+    use super::*;
+
+    #[test]
+    fn test_part_1() {
+        let sample = parse_input("samples/day08.txt");
+        assert_eq!(part_1(&sample), 21);
+    }
+
+    #[test]
+    fn test_part_2() {
+        let sample = parse_input("samples/day08.txt");
+        assert_eq!(part_2(&sample), 8);
+    }
+}